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This is a melting device. We used this device in the forging operation where Cast Iron, Bronze, and other alloying elements are melted.
This is a very old device we used in the manufacturing for melting because this system produces good cast iron from Pig Iron. The shape of this device is cylindrical but others size is also available.
While choosing cupola furnace we keep some valid factor that is- Melting Point Temperature, Shapes and many more.
The Cupola furnace works on the principle of combustion of coke generates (carbon dioxide and heat) and therefore it causes iron to melt. The melted iron gets a downgrade.
The charge introduced in the cupola consists of pig iron, scrap, casting rejection, coke, and flux. Coke is the fuel and limestone are added as a flux to remove undesirable materials like ash and dirt. The scrap consists of Steel and cast iron rejections.
Cupola Furnace Working:
Over the sand Bottom, Coke in charged extending up to a predetermined height. This serves as the coke bed within which the combustion takes place.
Cupola operation is started by igniting the coke bed at its bottom. After the Coke bed is properly Ignited, alternate charges of limestone, pig iron, and coke are charged until the level of the charging Door.
Then the air blast is turned on and combustion occurs rapidly within the coke bed. Within 5 to 10 minutes after the blast is turned on the first molten cast iron appears at the tap hole.
Usually, the first iron which comes out will be too cold to pour into sand molds. During the cupola operation, molten metal may be tracked every 10 minutes depending on the melting rate and the capacity.
All the oxygen in the air blast is consumed by the combustion, Within the combustion zone.
The chemical reaction takes place which is,
C + O2 (from the air) → CO2 + Heat
This is an exothermic reaction. The temperature in this zone varies from 1550 to 1850 degree Celsius.
Then hot gases consisting principally of Nitrogen and carbon dioxide moved upward from the combustion zone, where the temperature is 1650 degree Celsius.
The portion of the coke bed if the combustion zone is reducing zone. It is a protective zone to prevent the oxidation of the metal charge above and while dropping through it. As the hot carbon dioxide gas moves upward through the hot coke, some of it is reduced by the following reaction.
3Fe + 2CO → Fe3C + CO2
This is an endothermic reaction.
The first layer of iron above the reducing zone is the melting zone where the solid iron is converted into the molten state. A significant portion of the carbon is picked up by the metal also take place in this zone.
The hot gas is passed upward from the reducing and melting zones into the preheating zone which includes all layer of charge above the melting zone up to the charging Door.
Since the layer of the charge is preheated by the outgoing gases which exist at the top of the cylindrical shell. this temperature is this zone is around 1090 degree Celsius.
Construction / parts:
Legs are provided for supporting purpose there.
Slag Hole or Slag spout:
The slag hole is used for removing or extracting the slag from the melting iron.
This is in taper form and from this, the melted iron comes out easily.
By tuyeres, we enter the gas to proper burn of fuel.
In Preheating zone the heating process started and heats the metal charge about 1090 degree Celsius.
In the melting zone, we do not provide much heat to melt the metal charge because it’s already melted in the preheating zone with temperature about 1090 degree Celsius.
From here we supply the charge to the furnace. The various charges are for the cupola furnace-Pig Iron, Coke and limestone.
Brick lining and Steel shell:
The shell of the cupola furnace is being usually made of steel and it’s called a steel shell.
This device used in the system for preventing the emission from the fireplace.
Advantages, Disadvantages, Application of Cupola furnace:
- For operation purpose, this is a simple and economical device.
- A wide range of material can be melt.
- This device used for removing the slag present in the Iron.
- Comparison of electric furnace This is very less harmful.
- This is having high melting heat I.e 100 tones/hr
- Floor space required is less.
- and to perform the operation skilled operator not required.
- In cupola furnace, The main disadvantage is that sometimes unable to main the close temperature.
- A number of more types of cast iron is produced from this device like Malleable, Grey cast iron.
- The copper base alloy is also manufactured by this device.
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